PROJECT SUMMARY ! The abundance of airborne micron-sized pollutant correlates with the prevalence and severity of respiratory diseases, which represents the 3rd leading cause of death in the United States and have an economical cost of tens of billions of dollars per year. Growing concerns on the possibility of terrorist attacks have motivated efforts in preparing for and responding to airborne releases of chemical, biological or nuclear materials in highly populated regions. Experimental and computational techniques that can precisely correlate the fate of a contaminant with its initial release location are sorely needed to inform and validate the next generation of predictive tools in the area of contaminant dispersion. In Phase I of this project we demonstrated the potential of DNATrax (DNA Tagged Reagents for Aerosol eXperiments), a 2013 R&D 100 Award winning and FDA recognized technology, able to produce a virtually infinite number of distinct, DNA-labeled and environmentally safe micro-particles that can be used as contaminant simulants both indoors and outdoors. This paved the way towards a novel framework to inform, advance and validate numerical simulations of contaminant transport in both indoor and outdoor settings. To this end, in Phase II, we will significantly improve the accuracy of our methodology, expand the considered range of aerosol sizes, and demonstrate capabilities of tackling outdoor contaminant transport. Consequently, our specific aims are as follows: Aim 1: Enhance accuracy, repeatability, and flexibility of the experimental method. We will improve several crucial aspects of our methodology for predicting contaminant transport, including particle release, sampling, and analysis, as well as flow characterization using Particle Image Velocimetry (PIV) and aerosol transport modeling using LES. In particular, we will accurately measure the amount of deposited DNA copies after each release experiment, and we will compare with time-resolved simulations in which millions of Lagrangian particles are individually tracked using highly efficient parallel super-computing. Aim 2: Demonstrate the capabilities of DNATrax as contaminant simulant in outdoor releases. We will leverage the unique facilities and expertise at the Edgewood Chemical Biological Center to perform open air releases in a 400-acre plot of land monitored by meteorological stations, as well as releases in a 200 ft long breeze tunnel. In these large scale deployment of DNATrax we will employ the same experimental methodology which we will have refined in Aim 1 through small-scale wind tunnel measurements. Using our team's top-notch computational capabilities, we will perform highly resolved LES simulations of these large-scale release cases, including the complexities of the filed site terrain.